Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

“प0रा1 को छोड न' 5 तरफ”Jawaharlal Nehru

“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 14989 (2001): Recommended Practices for SeismicQualification of Electrical Equipment of the Safety Systemfor Nuclear Generating Stations [LITD 8: ElectronicMeasuring Instruments, Systems and Accessories]

IS 14989:2001,,j

IEC 60980 (1989) vr

—-...4.

Indian Standard

RECOMMENDED PRACTICES FOR SEISMICQUALIFICATION OF ELECTRICAL EQUIPMENT

OF THE SAFETY SYSTEM FOR NUCLEARGENERATING STATIONS

ICS 27.120.10;27.120.20

CI BIS 2001

BUREAU OF INDIAN STANDARDSMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

/

August 2001

,/

Price Group 12

——

Nuclear Instrumentation SectionalCommittee,LTD 26

NATIONALFOREWORD

This Indian Standardwhich is identicalwith IEC60980(1989)‘Recommendedpracticesfor seismicqualificationof electrical equipment of the safety system for nuclear generating stations’ issued by the InternationalElectrotechnicalCommission (IEC),was adoptedby the Bureauof Indian Standardson the recommendationofNuclear InstrumentationSectionalCommittee(LTD26) and approvalof the Electronicsand TelecommunicationDivision Council.

The text of the IEC standardhas been approvedas suitablefor publicationas Indian Standardwithout deviations.Certain conventions are, however, not identical to those used in Indian Standards. Attention is particularlydrawn to the following:

a) Wherever the words ‘InternationalStandard’appear referring to this standard, they should be read as‘IndianStandard’.

b) Comma (,) has been used as a decimalmarkerwhile in Indian Standards,the currentpractice is to use apoint (.) as the decimalmarker.

Only the English languagetext in the InternationalStandardhas beenretainedwhile adopting it in this standard.

CROSS REFERENCES

The technical committee responsible for the preparation of this standard has reviewed the provisions of thefollowing International Standardand has decidedthat it is acceptablefor use in conjunctionwith this standard:

IEC 60780 (1998) Nuclear power plants — Electricalequipmentof the safety system— Qualification.

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IS 14989:2001

IEC 60980(1989) ..-—

Indian Standard*,.*

RECOMMENDED PRACTICES FOR SEISMIC QUALIFICATIONOF ELECTRICAL EQUIPMENT OF THE SAFETY SYSTEM

~p’:,

FOR NUCLEAR GENERATING STATIONS

1 Scope and object

This standard is applicable to electrical equipment and the instrumentation and control equipment (I& C) of the safety system that is used in nuclear power generating stations including componentsor equipment of any interface whose failure could adversely affect the performance of the safetysystem.

This standard presents acceptable seismic qualification methods and requirements to demonstratethat electrical and I & C equipment can perform their safety-related functions during and after anearthquake. As seismic qualification is only a part of equipment qualification, this standard shall beused in conjunction with IEC 780.

2 Definitions

In addition to definitions contained in IEC 780, the following definitions establish the meanings ofwords in the context of their use in this standard.

In general, this standard is based on IAEA terminology.

2.1 Device

An item of electrical equipment that is used in connection with, or as an auxiliary to, other items ofelectrical equipment.

2.2 Assembly

Two or more devices including a common mounting or supporting structure.

2.3 Active equipment

Item for which the safety-related function is required to be performed by means of a mechanicalmotion or change of state.

2.4 Passive equipment

Item whose safety-related function is the maintenance of structural integrity and for which a changeof state is not required.

2.5 l14a@nction

The loss of capability of the equipment to initiate or sustain a required function, or the initiation ofundesired spurious action which might result in adverse consequences. Functional acceptancecriteria shall be specified by relevant specifications.

2.6 Natural frequency

A natural frequency of a structure or body is the frequency of its free vibrations depending only onits own physical characteristics (mass, shape, elasticity “and damping distribution) and restraintsand supports (see figure 1).

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1S 14989:2001

IEC 60980(1989)

2.7 Sine beat

A continuous sinusoidal wave of one frequency whose amplitude is modulated by a sinusoidalwave of a lower frequency as shown in figure 2.

2.8 Sine dwell

A continuous sinusoidal wave at a single frequency.

2.9 Test frequency

The frequency of the applied force by which the specimen is excited during the test.

2.10 Response spectrum

Plot of the maximum response, as a function of oscillator frequency, of an array of single-degree-of-freedom damped oscillators subjected to the same base excitation (see figure 4).

2.11 Narrow-band response spectrum

A response spectrum that describes motion in which amplified response occurs over a limited(narrow) range of frequencies.

2.12 Broad-band response spectrum

Response spectrum that describes motion in which amplified response occurs over a wide (broad)range of frequencies

2.13 Required response spectrum (RRS) ----

Response spectrum issued by the user as part of the specifications for proof testing, or artificiallycreated to cover future application. The RRS constitutes a requirement to be met (see figures 1 and !

2).

2.14 Test response spectrum (TRS)

Response spectrum that is obtained from the actual motion of the shake table by analyticaltechniques or by spectrum analysis equipment.

NOTE - In equipmentqualification,the TRS shall be comparedto the RRS (see figure 1).

2.15 Power spectral density (PSD)

Mean squared amplitude per unit frequency of a waveform. PSD is expressed in g2/Hz versusfrequency for acceleration waveforms.

2.16 Preferred testing axes

Three orthogonal axes which correspond essentially to the most vulnerable axes of the specimen.

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IEC 60980(1989)

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2.17 S1 earthquake*

Earthquake which could affect the location during the operating life of the equipment to be1

y’,,qualified. For this type of earthquake, components shall be designed to continue to operate withoutmodification.

$

2.18 S2 earthquake*

Earthquake which produces the maximum vibratory ground motion for which certain structures,systems and components are designed to remain functional. Those are essential to assure properfunction, integrity and safety of the total system which is to be qualified.

2.19 Floor acceleration

Acceleration of a particular building floor or level resulting from a specific earthquake’s motion.

2.20 Zero period acceleration (ZPA)

Acceleration level of the high frequency, non-amplified portion of the response spectrum. Thisacceleration corresponds to the maximum peak acceleration of the time history from which thespectrum is derived.

2.21 Significant cycle

Cycle for which the amplitude range is between 50 % to 100% of the maximum amplitude of themotion.

2.22 Quull~cation testing

Seismic qualification testing means subjecting the equipment to a suitable vibratory input motion so.,

as to ensure that the equipment is capable of withstanding vibratory loads equal to or greater thanthose produced by seismic event(s). The seismic events are normally represented by the required ~response spectrum.

2.23 Fragility

Susceptibility of equipment to malfunction as a result of structural or operational limitation, orboth.

2.24 Fragility level

Highest level of input excitation, expressed as a function of input frequency, that equipment canwithstand and still perform the required safety related function. The fiagilit y level can be expressedin terms of response spectrum (fragility response spectrum FRS) that is a TRS obtained from teststo determine the fragility level.

* The definitionsof S1and S2 earthquakesgivenby IAEASafetyGuide50-SG-S1 are:

- Ground motion level 1 (S1):Maximum ground motion which reasonably can be expected to be experienced at the site area once during theoperatinglife of the nuclearpowerplant.

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1

- Ground motion level 2 (S2):Groundmotion which is consideredto be the maximumearthquakepotentialat the site area.

IS 14989:2001 -——

IEC 60980(1989),,!

3 Earthquake environment and equipment response‘--7

%..

This clause is intended to provide information on earthquake behavior and on the dynamic

7

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performance of equipment during earthquakes and simulated seismic events. Numerical values are~i,+

typical and illustrative but should not be considered as standards.*;]

3.1 Earthquake environment

Earthquakes produce random ground motions which are characterized by simultaneous butstatistically independent horizontal and vertical components. An earthquake of magnitude 6 orhigher on the Richter scale may persist for 15 s to 30s and produce a maximum horizontal groundacceleration from 0,1 g to 0,6 g or higher with the major energy content usually occurring in thefirst 5 or 10s. The typical broad-band random motion occurs over a frequency range from 1 Hz to35 Hz.

3.2 Equipment on foundations

Amplitude of the ground motion (both horizontal and vertical) can be magnified in foundation-mounted equipment. For any given ground motion, the magnification depends on the system’snatural frequencies of vibration (soil, foundation and equipment) and the mechanisms of damping(see 3.6). The typical broad-band response spectra that describes the ground motion indicates thatmultiple frequency excitation predominates.

3.3 Equipment in structures

The ground motion (horizontal and vertical) may be filtered and amplified by intervening structuresto produce different motions. The dynamic response of floor-mounted equipment may reach anacceleration man y times that of the maximum ground acceleration, depending upon the systemdamping and natural frequencies of vibration. The magnification and bandwidth depend upon thedynamic response characteristics of each building and equipment structure. .-..

3.4 Simulating the earthquake

\The goal of simulation is to reproduce the effects of the postulated earthquake motion as closely aspossible.

The form of the simulated seismic motion used for the qualification of equipment, by analysis ortesting, can be described by one of the following: time history, response spectrum, or the powerspectral density (PSD) function. These data may be generated for the structures upon which theequipment is to be mounted. They are supplied by the user or his agent to the manufacturer as apart of the specifications for that equipment (see clause 5) or provided by the manufacturer to coverfuture applications.

Because of the directional nature of seismic motion as well as the filtered output motion ofstructures, the directional components of the motion and their application to the equipment shouldbe specified.

3.5 Time history

The expected form of the motion is obtained from existing earthquake records or may be artificially”generated. For application at any floor, the time history record generated includes the dynamicfiltering and amplification effects of the building and other intervening support structures (seefigure 5).

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IS 14989:2001

IEC 60980(1989). .. —-. ..-

3.6 Damping

Damping is the generic name ascribed to the numerous complex energy dissipation mechanisms ina system. In practice, damping depends on many parameters, such as the structural system, modeof vibration, strain, force in normal situations, speed of application of this force, materials, jointslippage, etc.

In linear vibration theory, the simplifying assumption is made that damping is purely viscous, ordependent on the relative velocity of moving parts. Therefore, when a value of damping isassociated with a practical system, it is usually assumed to be equivalent viscous or linear dampingwhich is a convenient simplified way of relating real-world hardware behavior, which may be non-linear to some degree, with theoretical concepts which normally utilize linear methods of analysis.

4 Seismic qualification requirements

4.1 Introduction

The seismic qualification shall demonstrate the safety system equipment’s ability to perform itsrequired function during and/or after the time it is subjected to the forces resulting from one S2earthquake. In addition, the equipment should withstand the effects of a number of S 1 earthquakesprior to the application of an S2 earthquake (see clause 6).

Qualification of electrical’ items of the safety system for nuclear power generating stations is fullydescribed in IEC 780 and, in particular, clause 4 of that standard describes the principles ofqualification. Seismic testing shall be performed in the proper test sequence with the environmentaltesting where required (see annex A). This standard may be used by equipment manufacturers toestablish procedures that will yield data to substantiate performance claims or by equipment usersto evaluate and verify performance of representative devices and assemblies as part of an overall ..qualification effort.

In summary, qualification is a formal Process bv which the reauired demonstration is achieved in kan unambi~uofis recorded and traceab~e manner-so that its applicability and validity can readily beconfirmed.

4.2 The process of seismic qualification

Due to its formal nature, seismic qua~ificationclause 5). These are :

will include a number of recognizable steps (see

4.2.1 Specification of the equipment to be qualified

The equipment shall be clearly specified.

The specification shall include:

- a description of the equipment, its type number, drawing and issue number, specification, etc.;

- the boundaries of the equipment to be qualified, for example: which input/output connectionsare involved, which mountings are to be included or excluded, etc.;

- the operating conditions (loadings) which are necessary;

- ageing conditions according to 5.3.3 and 5.3.5 of IEC 780, see also 5.3.3 of this standard.

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IS 14989:2001

IEC 60980 (1989)

4.2.2 Specification of theseismic requirements

...- .—

..4

These requirements shall be clearly speciiled. They shall include at least:

- time duration;- frequency range;- acceleration values.

Information which provides these data may be:

- vibratory motion in terms of power spectral density as a function of frequency;

- the strong motion time duration of the earthquake;

- the required response spectrum (RRS) for the fixing points on which the equipment will bemounted. The RRS shall include data for the principal horizontal axis and the vertical axis, andshould be specified for 2 %, 5 % and 7% damping ratio;

- maximum accelerations versus significant frequencies, or time history of the fixing point onwhich (floor or structure) the equipment will be mounted

- details of the multiple S2 requirements (see 6.2.9.2).

In evaluating the seismic risk of a particular site, it may be necessary to make an allowance for theestimated number of S 1 and S2 earthquakes to which the specimen might be subjected during theinstallation’s lifetime. Five S 1 and one S2 earthquakes are generally assumed unless a differentnumber can be justified. However instead of five S 1 a specimen may be subjected to Iwo testscorresponding to level S2.

S 1 seismic tests shall be followed by at least one S2 seismic test and the duration of each test waveshall be at least equal to the strong part of the time history used to define the RRS. If no timehistory is given, 10 significant cycles for the seismic tests should be used unless otherwisespecified.

The test waves simulating S 1 or S2 earthquakes maybe applied as “wave train”. In this case, thewaves shall be sufficiently spaced by at ‘least 2 s to avoid superimposing their effect on theequipment.

4.2.3 Specljication of acceptance criteria

These are the factors on which the successor failure of qualification will be judged.

They shall be clearly specified and may indicate whether the equipment is to operate during the testor merely to survive and operate afterwards, and include:

- a listing or description of the safety functional requirements;

- a list of acceptance criteria in order to remain functionafi

- identification of margins;

- any particular requirements for tests or analysis.

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IEC 60980(1989)

4.2.4 The qualljication tests or analysis

The equipment defined in 4.2.1 shall be qualified to meet the requirements defined in 4.2.2.~

~F “

Succes_s ~r failure shall be judged by means of the criteria specified in 4.2.3.,

Some general methods to achieve this qualification are described in IEC 780:

- Qualification by analysis or combination of test and analysis in which the performance of theequipment is predicted without physical test or on the basis of existing data (see 5.3.2).

- Qualification by testing in which a typical example of the equipment is tested (see clause 6).

- Qualification by experience. Although not yet an established technique, recent data indicate thatqualification by experience maybe a valuable method of seismic qualification. This method isdescribed in the annex A for guidance.

Each of the preceding methods, or other effective methods, maybe adequate to verify the ability ofthe equipment to meet the seismic qualification requirements. Seismic qualification analysis (SQA)(tests, analysis or combination of both) establishes the particular procedures whose choice shouldbe based on the practicality of the method for the type, size, shape and complexity of theequipment.

4.2.5 Provision of documentation

Clear and complete documentation shall be provided (see clause 7). This is an essential part ofqualification. Its purpose is to demonstrate that the equipment meets performance requirementswhen subjected to the seismic accelerations for which it is to be qualified.

5 Seismic qualification analysis (SQA)

The seismic qualification analysis covers the methods to rationalize the operations (tests, analysisor combination of both) and ensures that sufficient margin accounts for the uncertainties.

The SQA assumes that the equipment will perform its intended functions if the sub-assembly andthe correlative interfaces accomplish their respective functions under the conditions resulting from:

- the mutual coupling of the sub-assembly;

- the seismic loading induced by the seismic excitation required for the equipment;

- the loading related to the functional requirements of the equipment.

The effects of the above conditions on the sub-assembly shallsimultaneously. Each sub-assembly may be considered separately.

SQA includes four successive steps, which are detailed hereafte~

- equipment review, sub-assembly selection;

- sub-assembly review, boundary conditions and interactions;

be considered as acting

- qualification operation, tests or computations or a combination of both;

- synthesis, results and margin evaluation.

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IEC 60980 (1989)

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5.1 Equipment review __.—.+

The purpose of this step is:

1~;;,

to divide the actual equipment into several significant sub-assemblies (one or more, idealizedor physically independent) (see figure 6);

to determine the set of sub-assemblies which is representative of the actual equipmenu

to identify the sub-assembly which may be affected by modifications or alternateconfigurations.

The aim is to reconcile:

- the availability of test and computation facilities;- the reliability of the results obtained in the qualiilcation process;- the optimal use of available data.

Sound engineering judgernent is necessary; however, any erroneous choice would be revealed bythe”subsequent steps, so that the final conclusion cannot be affected.

5.2 Sub-assembly review - Boundary conditions and interactions

The purpose of this step is:

- to identify the function of each sub-assembly required for the adequate performance of theequipmen~ all the operating modes and postulated events shall be considered;

- to establish the loadings at interfaces for each sub-assembly and determine their significance.. .

5.2.1 Coupling

The behavior of sub-assemblies maybe different, according to whether they are normally linked to \

the equipment or physically separated. Coupling effects induced by seismic events shall beexamined.

5.2.2 Seismic loading of sub-assemblies

When the selected sub-assemblies are not directly mounted on the equipment support, they aresubject to a seismic loading which shall be established on the basis of the following elements:

- the dynamic transfer properties of the sub-assembly supporting structure;

- the specified seismic loading of the equipment (usually defined by the RRS);

- a justifiable method of test, calculation or a combination of both.

Some of these methods are detailed in the following and shown in figure 7.

5.2.2.1 Experimental method

The specified seismic motion of the equipment support is simulated and the response in points ofinterest of the specimen is monitored (local response).

NOTE - Complementary analysis may be necessary to assess the representativenessof the specimen and testconditions or to amend the experimentaldata to account for coupling effects or alternativeconfigurationsof theequipment.

8

5.2.2.2 Calculation method

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IS 14989:2001

IEC 60980(1989) .._;

In a first stage, the modal parameters are identified by analyses depending on experiments or,<,

calculation.

Then, the local response of the equipment at points of interest maybe determined, for example by:

- direct response spectra transfe~

- response of individual modes and superimposed effects.

NOTE - Tests may be necessaryto verify the results of the complexmathematicalmodels or to determinemodalparametersfor a betterapproximationto reatity.

The seismic loading of the sub-assembly can be expressed in terms of RRS.

To account for analysis uncertainties and experimental errors, the peaks of the response spectrashould be enlwged and broadened by a justified factor.

5.2.3 Loading

The loading is expressed by the physical conditions applied to the sub-assembly. In addition, theinfluence of the location and orientation of each sub-assembly shall be taken into account.

5.2.4 Properties of the sub-assemblies

- Linearity

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The physical properties or the response of the sub-assemblies may be non-linear for examplestiffness and therefore modal frequencies may change with stress level. In this case, the appropriateconsiderations will restrict the validity or mitigate the errors in experimental data or linearassumptions of models.

- Damping

Different damping values may be associated with the same constituent according to:

- stress levels (non-linearity effect);- modes of vibration.

Unless other documented evidence is available, the following damping factor maybe assumed:

- Control panel, cabinets: 7 % of ctitical darnping (when welded 4 %)

- Motors: 2 % of critical darnping (when welded 4 %)

- Cable trays: 10% of critical damping (when welded 4 %)

If a device cannot be identified, a damping value of 5 % is suggested.

.,

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IS 14989:2001

IEC 60980(1989)-p.-

5.3 Qu.alijication actions

.?~’:’;.

The purpose of this step is to provide sufficient evidence and information on the behavior of thesub-assemblies, with the aim of demonstrating in the following step (synthesis) that the equipmentmay perform its safety functions under postulated seismic conditions.

The operations on the sub-assemblies shall be planned in order to investigate all the potential failuremodes and malfunctions, which may be categorized as below:

- rigidity: the failure is related to the intensity of the seismically induced excitation (e.g.structural integrity);

- resonance: the failure is related to the intensity and frequency content of the seismicallyinduced excitation (e.g. chatter of electrical contacts);

- cumulative damage: the failure 4s related to the intensity, the frequency content and the numberof load cycles induced by seismic excitation.

Tests or computation maybe used to investigate the behavior of the sub-assemblies.

Tests may be suitable for some sub-assemblies or particular simulations, and computation for someothers. The following table illustrates the factors affecting this choice. An appropriate conservativemargin shall be considered whenever the investigation method produces approximate results.

Method

Tests

I

LComputations

5.3.1 Tests

Suitable field of investigation

Complex functionalinput-outputrelationships

Indeterminatefailuremodes

Dynamicperformance

Postulatedfailuremodes(structuralintegrity)

Extrapolationand interpolationofdynamicperformance

Main accuracy factor

Test conditions (motion, type,environmentsimulation)

Specimenrepresentativeness

Size,couplingeffects,functionalsimulation

Mathematicalmodelaccuracy

Analysismethod(staticequivalent,modalanalysis,modal spectralanalysis,etc.)

Usual margin

Severityof testloading

Safetyconditions

The procedures used to perform the tests are detailed in clause 6.

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5.3.2 Computations..+

Computation may complement tests, to extrapolate or interpolate experimental data. Computation

q

“$,., ,may also investigate established failure modes related to structural integrity, fatigue and stress-

+

strain behavior.

Two methods of computation are suggested below:

- static equivalent load, which yields conservative results in return for the crude approximationof the mdel;

- dynamic analysis, which takes into accountcan be suitably represented by linear models.

5.3.2.1 Static equivalent load calculation

the modal properties of the structure and which

The passive sub-assembly may be assumed to be subject to a constant and uniform equivalentacceleration as specified below:

a) The fundamental frequency of the sub-assembly is established for each main orthogonal axisby calculation, modal testing or analysis.

b) For each orthogonal axis, the applicable RRS (acceleration) is used to determine themaximum peak value within the interval of uncertainty of the fundamental frequency (see figure8).

NOTES1)The intervalof uncertaintyis estimatedon an errorcalculationbasis.2) If little or no frequencyinvestigationhas beenperformed,the uncertaintyintervalis wide and the maximumpeak value (MPV)of the applicableRRS shall be selected.3) If evidencecan be producedthat the consideredpart is rigid, theZPA valuecan be selected.

.-

c) For each axis, the equivalent acceleration values result from the above maximum values &multiplied by 1,5, or less if justified, to account for the effects of the neglected modes.

d) For both. directions of each main orthogonal axis, the relevant equivalent acceleration isapplied to the masses of the considered sub-assembly to simulate the seismic loading.

e) The same seismic effects along each main orthogonal axis are superimposed, according to thesquare root of the sum of the squares.

5.3.2.2 Dynamic computations

The dynamic computations are based on three methods:

- a calculation method, usually implemented by a computer routine, to determine the modalparameters;

- a mathematical model of the considered structure and sub-assembly (often a finite elementmodel or transfer matrix or other justifiable method);

>- a calculation method to establish the effect of the modes under the action of applicable seismicloading (usually by spectral analysis).

NOTE - Modal testing mayreplacemethods 1and 2 and providethe modalparameters.

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IEC 60980(1989)

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Justification shall be provided for the following points:

- Calculation methods

. Basic principles of the method

. Validation of the computer routines

. Procedure for combining modal responses and directional responses.

- Model assumptions

. Idealization principles

. Distribution of the model elements, number of dynamic degrees of freedom

. Values of parameters

. Non-linearity effects

. Damping.NOTE - Tests may be advantageousto refineassumptionsabout damping, linearity, stiffness, etc.

- - Results from the calculation method and the correlated model

. Number of modes taken into account and total of equipment mass

. Effect of neglected rigid modes

. Accuracy.NOTE - Tests may be necessaryto vatidate these results.

5.3.3 Ageing

Age conditioning is required for those sub-assemblies having ageing mechanisms which maysignificantly affect the seismic behavior. In this case, a qualified life objective shall be determined,age conditioning shall be performed, prior to other simulation or investigation tests. --

5.3.4 Inte@aces k*

Contiguous elements may significantly interact with the considered sub-assembly. Attention will bepaid to the support characteristics and the functional connections (such as cable trays, piping, etc.).

5.3.5 Specimen

When necessary, the simulations will be performed on specimens as representative as possible ofthe in-service conditions. However, alterations are acceptable in the following cases:

- The alteration of the specimen is not in conflict with the purpose of the simulation (for exampledummy devices may simulate the mass distribution of a supporting structure to determine themechanical transfer functions by vibration tests).

- The effects of the alteration can be predicted with reasonable precision.

5.3.6 Severity

Simulations and investigations on the sub-assemblv shall consider the most severe combination ofthe loadings identified [n step 2 of the SQA (seis~c and functional loadings). To encompass the Imost expected modifications, or to take into account multiple applications, the sub-assembly shouldbe qualified with a sufficient severity margin.

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5.4 Synthesis

The purpose of this step is to verify the following points:

- The actual equipment is suitably represented by the set of sub-assemblies whose seismicbehavior has been investigated and documented.

- For each representative sub-assembly, the loadings assumed in the investigations meet orexceed the actual in-service conditions and the seismically induced excitation of the equipment.Coupling effects between sub-assembly shall be included.

- The investigated performance of each sub-assembly conservatively enable the equipment toperform its safety function(s).

Synthesis is used to establish whether the qualification requirements are satisfied for equipmentwhich shows some analogous properties with previously qualified equipment.

The following examples in figures 9 and 10 illustrate some suggested procedures.

6 Seismic test qualification

6.1 Introduction

The procedures indicated in this clause should be used for the seismic cmalification testinsz of thesafe[y system or other equipment designed to withstand earthquakes. ‘

In general, a seismic test qualification program is recommended for complex assemblies (for which-,

qualification by analysis is not possible) or for equipment in which possible malfunctions arerelated to functional performances. Therefore, the equipment should be tested under simulated ~operating conditions. The seismic test shall be performed by subjecting the specimens to avibratory motion which conservatively simulates that to be seen at the equipment mounting locationduring the considered dynamic event.

A practical problem in attempting to define tests for qualifying specimens is in the selection ofsuitable testing waves, as detailed in 6.5. Numerous factors shall be taken into account includingthe type of specimen, its location and the nature of the earthquake expected, etc.

A further point of consideration is to determine whether the specimen is to be used for a uniqueapplication or for a more general purpose. In the first case, the seismic motion can be specified andthe qualification testing selected to comply with the specification (proof tests), whereas in the lattercase, the test shall be designed to qualify the specimen for future application, for which a moregeneral seismic input motion would be specified (fragility tests). Another difficulty arises whenattempting to define the testing of individual components (relays, motors, sensors, etc.) or complexassemblies such as control cabinets.

The theoretical basis for test procedures is considered to be outside the scope of this standard, butcan be readily obtained from relevant technical literature.

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6.2 Test conditions

The seismic qualification test program shall include the following elements:

- seismic loads and test sequent%- input motion;- mounting conditions;- operational loads and operating conditions (for example voltage, pressure);- monitoring of output response and functional performance of the equipmen~- demonstration of operability.

6.2.1 Seismic loads

Generally the seismic loads are defined by a required response spectrum (RRS). It is usuallybroadened in the maximum amplification area to cover the effects of unknown or variable factorssuch as the natural frequencies of the building structure which are not known with accuracy, or thespecimen’s position inside the building.

The requirements should state the extent to which the spectrum is broadened; if not, the RRS shalIbe considered broad-band. RRS does not give information about the duration of the correspondingtime history and on the number of significant cycles.

These values should be specified. If not, the duration shall be not less than 30 s (except as noted)and the number of signifi~ant cycles shail range between 5 and 10.

6.2.2 Input motion

The input motion as described in 6.5, that shall be applied to the basederived from the RRS in order to satisfy the criteria of 6.5 and 6.2.9.3.

6.2.3 Mounting

of the specimen, shall be

The equipment to be tested shall be mounted on the vibration table in a way that simulates theintended service mounting. The mounting method shall be the same as that recommended for actualservice. The mounting method shall use the recommended bolt size and configuration, weld patternand type, etc. The effect of electrical connections and sensing lines, etc., shall be considered. Theorientation of the equipment during the test shall be documented and shall be the only orientationfor which the equipment is qualified unless adequate justification can be made to extend thequalification to an untested orientation. The method of mounting the equipment to the shake tableshall include a description of any interposing fixtures and connections. The effects of such fixturesand connections shall be evaluated if they are only used during qualification and not for in-servicemounting.

6.2,4 Loading

Seismic qualification tests on equipment shall be performed with the equipment subjected to normaloperating conditions. These shall include electrical loads, mechanical loads, thermal loads,pressure, etc., as far as they adversely affect the function.

The necessity and possibility of reproduction of full operating loads shall be evaluated for each

k

equipment s;bmit~ed to seismic test and the documentation-shall demonstrate that the partialreproduction (or non-reproduction) of the loads will not invalidate the results of the tests.

14

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IS 14989:2001 .--—...—

IEC 60980(1989)

6.2.5 Monitoring —-$-?{

Sufficient monitoring equipment shall be used to evaluate the functional performance of the I

equipment before, during (when required) and after the test. In addition, enough vibrationmonitoring equipment shall be used to allow determination of the applied vibration levels. In

~

~ ‘::

addition to monitoring the vibration table, it is recommended that as many points are monitored onthe equipment itself as may be needed to provide information to evaluate the vibration behavior ofthe specimen. These data can also be used for future evaluation of the qualification of theequipment for other applications and future changes, or for qualification of devices mounted on theequipment (for example instrument mounted on panel). The location of the monitoring sensorsshall be documented including photographs.

6.2.6 Demonstration of operability

According to the criteria of clauseperform its safety related function.

6.2.’7 Test sequence

4 during and/or after the seismic tests, the equipment shall

In general, seismic tests should be conducted according to the following sequence and as describedin the relevant specification:

a) Preliminary inspection in order to check the integrity of the equipmentb) Functional check (prior to the test)c) Vibration response investigation (exploratory test)d) Seismic qualification test including functional checke) Functional check (after the test)f) Final check.

The sequence of seismic tests within the global qualification process is identified in IEC 780.

6.2.8 Vibration response investigation

The specimen should be subjected to a vibration response investigation to determine its dynamiccharacteristics and as an aid in the justification of the test method chosen or for the results of thetest.

The vibration response investigation supplies data on the natural frequencies, and on the dampingof the equipment, and is useful in the choice of single or multiaxis testing.

The test shall be in the form of single axis excitation at low input vibration levels (lower than therequired dynamic qualification level). The test shall be performed (in each principal axis) in thefrequency range equal to or greater than those specified for seismic input motion (see 6.2.2).

The exploratory test can be performed in different ways, by base excitation or by impedancemethods.

6.2.8.1 Exploratory test by fixing points excitation

The most common method employed is a continuous sinusoidal sweep input at low levelacceleration with the frequency sweep rate not greater than 2 octaves per minute (1 octave perminute is often used). The selected acceleration level should be such as to obtain a good signal tonoise ratio for test facilities (normally, this value is chosen to be in a range between 0,1 g to 0,2 g).

Similar results can be obtained carrying out the resonance search by low level broad-band periodicrandom motion.

/

15 I

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IS 14989:2001

IEC 60980(1989)

6.2.8.2 Exploratory test by impedance method

The resonance search can be carried out by exciting the structure with movable shakers or byimpact testing. The signal coming from monitoring instruments (accelerometers, strain gages, etc.)shall be recorded and analyzed in order to obtain the responses curves of the equipment (i.e.acceleration versus frequency, or better the transfer function between responses and excitation).These curves show the resonant frequencies of the equipment,

For the test of 6.2.8.1 and for this test, it should be noted that:

- due to physical complexity or restricted access to critical parts, the exploratory tests may notdetect all the critical frequencies;

- because of non-linearities, resonance responses at high levels may differ in frequency anddamping from those recorded at lower levels and then some resonances may not be visible atlow excitation. The result of a low-level exploratory test may, therefore, not always providevalid information regarding the specimen’s dynamic response;

- when an exploratory test is selected in order to justify the chosen test qualification method ofsingle frequency waves, it may be useful to carry out vibration response investigation at twodifferent levels in order to indicate non-linearity.

Resonance search at two different levels may also be useful to justify qualification by acombination of analytical and test methods.

In any case, if the configuration of the equipment is such that frequencies cannot be ascertainedwith reliability, the testing method shall be one of those described in 6.5.2.

6.2.9 Qualification test method

6.2.9.1 General

As is well known, seismic excitation occurs simultaneously in all directions in a random way.According to this point of view, the test input motion should consist of three mutually independentwaveforms applied simultaneously along the three orthogonal axes of the equipment.

However, taking into account that three axial testing installations are rare and that triaxial testing isdesimble when significant coupling exists simultaneously between the two preferred horizontal axisof the specimens, biaxial testing with multifrequenc y independent input motion in the horizontaland vertical direction is an acceptable test. Tests shall be performed according to 6.3.2 and, interms of total duration and fatigue induced, are intended to become conservative.

In some cases, single axis tests with multiple or single frequency excitation are also acceptablemethods of test if properly justified considering the effect of coupling between axes.

6.2.9.2 S1 earthquake and S2 earthquake testing

Seismic testing specifications include the effect of one (or more) S 1 and S2 earthquakes. Five S 1tests are usually considered to be sufficient in the absence of more accurate information.

The purpose of multiple S 1 testing is to demonstrate that earthquakes which are most likely tooccur, are not detrimental to functional safety of the specimen’s performance and do not generatefdtigue or ageing conditions whose undetected presence could lead to defective performance duringa subsequent S2 earthquake.

16

IS 14989:2001.. . .. .

IEC 60980(1989)

:

I When the required number of operational checks of the specimen is high, it may be necessary tosimulate more S2 tests than specified to allow checking of the specimen part by part.

~-~q

NOTE - In such cases, fatigue at low number of cycles may be reveald, the test acceptance criteria of 6.2.13 ‘?

shall be modified in order to take into account the followingaspecc repairing without repetition of the completeseriesof tests is allowedproviding that the dynamiccharacteristicsof the specimendo not changesignificantly.

Ib Both the shape and magnitude of the spectrum may differ for the two seismic levels of S 1 and S2.

To qualify the specimen, it is therefore necessary to know the spectra corresponding to each of

Ithese seismic levels. It is commonly assumed that the S2 spectrum has the same shape as that for

]’the S 1 but twice as great.

For uniaxial or biaxial tests carried out according to 6.3.1 and 6.3.2, it is permissible to performthe required S 1 in the first step followed by the S2 repeating the same sequence with the remainingarrangements of the specimen.

6.2.9.3 Test response spectra (TRS) acceptability

Normally, random vibration or synthesized input waveforms should be used in carrying out the test(see 6.5.2).

The actual input motion obtained starting from RRS shall have sufficient intensity and duration insuch a way that its TRS envelops the RRS or the applicable portion of the RRS taking into accountthe dynamic characteristics of the equipment under test, i.e. the natural resonance frequency.

If resonance phenomena does not exist below 5 Hz, the RRS should be enveloped for frequency

values above 5/fl= 3,5 Hz.

In general, the TRS should envelop the RRS closely and should have a similar shape so thatfkquency characteristics of the input motion are consistent with the frequency content of the RRS.

If resonance phenomena exist below 5 Hz, it is accepted that the TRS stays below the RRSaccording to the limit of the vibration table provided that an alternative test is performed usingequivalent excitation methods (such as concentrated excitation), and their equivalence isdemonstrated.

In any case, the TRS shall envelop the RRS in correspondence with both the natural frequencies ofthe equipment under test and with high frequencies (ZPA). TRS shall be computed with 1/3 octave(or narrower) bandwidth resolution using justifiable analytical technical or response spectrumanalysis equipment.

6.2.9.4 Selection of damping

In order to compare TRS with RRS, any representative value of damping maybe employed, whichshould not necessarily correspond to the equipment damping. This damping value should be inprinciple equal for the two spectra. In some cases, however, when data from past qualification areused, two possibilities exist:

a) the TRS has a damping level greater than the RRS; in such a case if the other requirements ofclause 6 are satisfied the qualification is acceptable;

b) the TRS has a damping level less than the RRS; in this case it is necessary to reanalyze thedata prior to reaching a conclusion. One possibility is to analyze the test motion in order toproduce a TRS with the same damping as the RRS.

17

IS 14989:2001IEC 60980(1989)

.—.. ... .

If necessary, reference can be made to the damping level corresponding to the one measured on thespecimen or to a value selected as given in 5.2.4.

6.2.9.5 Fragility testing

Fragility testing is used to qualify equipment by determining its ultimate capability; suchinformation may be used to prove adequacy for a given requirement.

The methods of 6.5 can be used to establish ilagility data and to assure proper application.

A measurement of the equipment fragility level for a particular motion constitutes a demonstrationof its ultimate capability to perform that motion. For example, if the RRS is broad-band, themultifrequency fragility curve (TRS) at appropriate damping (6.2.9.4) should overlay the RRS andbe demonstrated to be higher than the required spectrum.

6.2.9.6 Proof testing

Proof testing is used to qualify equipment for a particular application or requirement. Specimensshall be tested in accordance with 6.5.

6.2.10 Assembly testing

It is normal to test large complex assemblies by simulating the most critical in-service conditions.In such a case, the specimen is subjected to the required seismic input motion while the operatingconditions are applied or simulated and while its performance is recorded during the tests.

This might, however, prove to be impracticable in the event of complex specimens, which mayinclude many devices forming parts of several systems and being connected to other equipmentsituated at numerous positions within the structure (i.e. control panels containing items belongingto different circuits).

The following alternative is allowed

- testing of the assembly with devices inoperative or simulated by an equivalent dummy load,and

- recording the response of devices at the point of installation in order to obtain response spectrathat will be used in the qualification of the devices.

If there are many devices mounted on different locations of different panels, it is suggested that therequired spectra be obtained as an envelope of the response spectra of the whole mounting location.(see 6.2.1 1).

The data so obtained can be compared with the data obtained from previous qualification or fromfragility data of the devices in order to verify that the RRS of the devices is lower than the TRSrequired in the application (see 6.2.11).

In assembly testing, the method described in 6.5.2 or any other justifiable method maybe used,

After testing, the assembly shall be inspected and the integrity of all the unmonitored devices, suchas cabling, checked.

-..__.+

.i

.- -

The purpose of installing inoperative devices is to ensure that the specimen possesses the samedynamic characteristics as in normal operation.

18

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IS 14989:2001

IEC 60980(1989)

In order to take into account the interaction between the assembly under test and the interfacedequipment, additional consideration of the dynamic interaction between the equipment can berequired (see clause 5). For example, the number of vertical sections of control or power panelsthat can be qualified by tests are of course limited. In this case, the dynamic interaction betweeninterfaced equipment shall be considered.

This requirement shall be evaluated according to the type of equipment and shall be defined on acase-by-case basis. Functional performance of the assembly submitted to qualification tests shall bedefined on a case-by-case basis.

6.2.11 Devices testing

Each device (relays, breakers, etc.) shall be subjected to testing while simulating its functionalbehavior.

Normally, the device is fixed to the vibration table in a manner that simulates the in-serviceconditions. The device shall be subjected to a seismic input motion enveloping the responseexpected on the mounting positions of the assembly items (see 6.2.10).

If not, the device should be installed on the vibration table in such a way as to ensure dynamicsimulation of the required installation and then should be subjected to a seismic motion equal orgreater than that required for the assembly.

Some types of assembly produce impact or rattling that generate high frequency responses at themounting location of the devices, and testing of devices with input motion obtained from test on theassembly is recommended.

The upper frequency values for the tests may be higher than 35 Hz (up to 100 Hz). Otherwise, it isnecessary to provide additional data in order to demonstrate that the test is conservative andpossible effects of impact and rattling have been taken into account.

Testing of devices may require a frequency range higher than 35 Hz (up to 100 Hz).

6.2.12 Testing method for a specimen without critical frequencies

If it can be shown that the equipment is not resonant in the frequency range of the amplified zone ofthe response, it can be considered rigid and may be tested statically or according to the criteria of6.5.3.

6.2.13 Test acceptance criteria

Inspection shall be made to check the integrity and performance of the equipment before, duringand after the test (according to the type of equipment).

The acceptance criteria shall be specified in advance and the following minimum conditions shallnot occur, as far as applicable:

a) structural failure or deflection which would inhibit or prevent performance of any safetyrelated function is not acceptd,

b) loss of output signal; for example open or short circui~

c) spurious or unwanted output for example relay contact bounce exceeding the specified limits;

19

4-

IS 14989:2001

IEC 60980(1989)

—...-

d) drift of set-point or trip setting greater than the specified accuracy over the full range;

e) calibration shift greater than the specified accuracy over the full range; this parameter need notbe determined during vibratory excitation;

f,) structural failure; for example broken or loosened parts or deformation resulting in loss offunction;

g) loss of required performance characteristics; for example inability to change state;

h) loss of pressure boundary integrity; for example leakage;

i) correct functioning may be required during and after the test or merely after the event.

Sufficient instrumentation shall be provided to monitor and record device performance duringvibratory excitation; i.e. in order to show that each of the above criteria have been satisfied.

Whenever these criteria are not met, the specific deviation data shall be evaluated according to therelevant specification for specific applications.

Equipment assemblies or devices which fail to give satisfactory test results shall be repaired,modified, or replaced but in any case the entire test of the equipment shall be repeated andsatisfactory results obtained. If devices are replaced during a test, they shall be replaced accordingto the general criteria of IEC 780, aged if necessary.

6.3 Single and multiaxis testing

6.3.1 Single axis testing

Single axis testing applied successively in the three preferred axes of the equipment can be justifiedin the following circumstances:

- when there is little or no coupling between the three preferred axes of the equipment taken inpairs;

- when the equipment is subjected only to single axis excitation due to its installation conditions;

- when the multidirectional excitation is taken into account by an appropriate scaling factor. Forexample, if an element is normally installed on a specimen which amplifies motion in a singledirection, or if the construction and/or mounting of a component restricts its motion to onedirection, a single axis test may suffice.

However, if testing in all three axes is not carried out, this shall be justified. Testing shall beperformed according to the criteria of 6.5.

6.3.2 Biaxial testing

Biaxial tests are normally intended as the application of input motion in the horizontal and verticaldirection. According to the type of testing installation available, two cases maybe encountered.

20

IS 14989:2001 —-.—..—

IEC 60980 (1989)

6.3.2.1 Biaxial installation-.

Using multifrequency waves (see 6.4a)), tests shall be carried out by applying independentsimultaneous excitation signals along the horizontal and the vertical axes of the specimen and

y

~,q*~:

repeated after a rotation of 90° of the specimen about the vertical axis. The TRS obtained along each,.ii

axis shall envelop the RRS according to the criteria of 6.2.9.3.

6.3.2.2 Single axis installation

If a biaxial installation is not available, a vibration table moving along an inclined plane with respectto the horizontal axis is acceptable, the installation plane remaining horizontal.

Since in this case the motion along the two directions is not independent, four tests are thenperformed in order to test in and out of phase. The specimen shall be installed on the vibration tablein the positions indicated below:

- Position 1: specimen in position with one of the chosen horizontal axes along the direction ofexcitation

- Position 2: specimen rotated through 180° about the vertical axis from position 1

- Position 3: specimen rotated through 90° about the vertical axis with respect to position 1

- Position 4: specimen rotated through 180° about the vertical axis with respect to position 3.

With this type of test, the spectra obtained have the same shape for all three axes of the specimenbut with relative horizontal to vertical levels determined by the slope of the vibration table.

Normally this type of table has a slope of 45° but in some cases may have a different slope in therange 25° to 45°. .--

The TRS projected along each one of the two axes of the test specimen shall envelop the RRS ofthe corresponding axis according to the criteria of 6.2.9.3. This test maybe conservative since the hexcitation peaks are occurring simultaneously along both axes.

6.3.3 Triaxial testing

The test is performed with simultaneous input waveforms along two orthogonal horizontal axesand vertical axis of the specimen, each producing a TRS that envelops the corresponding RRSalong that axis according to 6.2.9.3. Two cases may be encountered according to the type ofinstallation available.

6.3.3.1 Triaxial installation

The test is performed with simultaneous but independent input waveform into the three preferredaxes of the specimen.

6.3.3.2 Biaxial installation (vertical - horizontal)

As tnaxial installations are rare, at present the use of a biaxial vibration table with independent I

simultaneous excitation signals in the horizontal and vertical plane is suggested. I

21

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IS 14989:2001

IEC 60980(1989)

- The specimen should be mounted and tested on the vibration table with the preferred horizontalaxis parallel to the excitation.

- Then, the equipment is rotated by 90° around the vertical axis and tested again.

- The specimen should then be mounted on the vibration table with one of the chosen horizontalaxis at 45° with respect to the excitation axes and tested.

- Then, the equipment is rotated 90° around the vertical axis and tested again.

The excitation level in the horizontal plane shall be adjusted in order to obtain a TRS that envelopsthe RRS along the two chosen orthogonal horizontal axes of the specimen (see 6.2.9.3).

If independent random inputs are not used, and a single axis installation such as described in6.3.3.2 is available, four tests should be run. The specimen is mounted on the vibration table asdescribed above according to the excitation axis and tested. The specimen is rotated into fourdifferent positions as discussed in 6.3.2.2.

6.4 Test wave selection

The selection shall take into account the anticipated ch?~actenstics of the specimen in its installedposition and under the influence of the specified earthquake. Whichever waveform is adopted, thetest response spectrum shall envelop the RRS or its significant portion thereof.

The test waves can be divided into two categories:

a) Multifrequency waves:

- Random vibration- Time history (synthesized or not).

b) Single frequency waves:

- Sine dwell- Sine beat- Sine sweep- Other waveforms (requiring justification).

6.5 Testing waveforms

6.5.1 General

Whichever test waveform is used, it shall:

- produce a TRS that envelops the RRS over the test ilequency range - TRS and RRS shall becompared to the same damping value or with a damping value of TRS greater than that of theRRS;

- possess a peak acceleration value equal or greater than the ZPA of the RRS;

- ideally not include any frequency greater than the maximum specified by the RRS.

22

--4‘

m

I

I

IS 14989:2001——.._-

IEC 60980(1989)

-. —.-i. .

6.5.2 h4ult.ifrequency ~esting “]

Multifrequency testing waves shall beinaccordance withthe mlesindicatedin 6.5.1 and6.2.9.3.q

ijw”,,

In order to develop a multifrequency waveform, different techniques maybe used according to the,,

‘!

test control system available (digital or analog).

6.5.2.1 I?andom signal test

The random signal test is performed by applying a random wave to the specimen adjusted to thefrequency range defined by the RRS at a level such that the TRS envelops the RRS according to5.2.9.3. If the method is used with an analog system, the level is adjusted to 1/3 octave bands withthe bandwidth of each band defined according to the equipment available.

If a digital system is used, the signal is adjusted at intervals of 1/3 octave (or narrower) 1. In thisway, it is possible to develop a suitable TRS without using an excessive maximum accelerationlevel as in the case of an RRS having low ZPA and high amplification. The signal is the result ofthe combination of narrow band components superimposed on a broad-band motion at thenecessary level. Other possibilities for obtaining a TRS that envelops the RRS closely m-edescribedin 6.5.2.1 and 6.5.2.2.

6.5.2.2 Random signal with superimposed single frequency signals

When the RRS shows low level ZPA and high amplification, it is acceptable to adjust the randominput at a level not substantially greater than that required to meet the ZPA and then superimposesingle frequency signals such as sine-dwell or sine beat to meet the response spectra according to6.2.9.3.

The bandwidth of the spectrum may require sine-dwell or sine beats at more than one frequency.----

They shall start simultaneously and their duration shall be equal to the test duration (sine beats shallbe spaced). The iiumber of cycles per beat may be adjusted in order to meet the requirements. ~

If the bandwidth of the RRS has been artificially broadened, a series of tests having different singlefrequency sine dwell or sine beats superimposed on the basic random motion w allowed providedthat complete justification is given.

6.5.2.3 Time history tesl

The test is performed by applying a previously synthesized time-history to the specimen (see figure4) to simulate the specimen’s probable excitation. The waves can be obtained by a combination(summation) of individual narrow band components superimposed on lower level broad-bandrandom motion.

This approach is suitable for a digitally controlled system which is allowed to obtain a table motionwhose TRS envelops the RRS according to the criteria of 6.2.9.3 without introducing an excessiveZPA level.

Different techniques can be used according to the computer program available. The first one isreadily used in a computer-controlled installation.

1 The suggested“~ue~ me 1/3 ~c~ve for 10 % or greater&mping, 1/6 Wwve for dampingbetween 2 % and 10 %and 1/12octave for dampingof 2 %’o or less.

23

IS 14989 :2001

IEC 60980(1989)

- Combination of multiple sinewaves

.——.-

The signal consists of a summation of multiple sinewaves at distinct frequencies controlled inamplitude and randomly phased in order to meet the requirements of 5.2.9.3. All sinewaves shallstart simultaneously and continue for the durdtion of the test. The frequencies are spaced at 1/3octave (or closer).

When the method is used in order to meet broad-band response spectra, tlhe results are very similarto broad-band random motion.

- Combination of sine beats

The method is similar to the above, but uses a combination of sine beats continuously repeated forthe duration of the test.

- Combination of decaying sine waves

The multifrequency wave is obtained as an aggregate of decaying sine waves startingsimultaneously and continuously present for the duration of the test. In this case, the undampedfrequencies of the component waves are also spaced 1/3 octave apart (or closer).

6.5.3 Single frequency testing

The single frequency wave shall produce a motion such that TRS, at the test frequency, is larger orequal to the RRS. The peak acceleration shall be at least equal to the ZPA of RRS except at lowfrequencies for which only the RRS value should be met (see 5.2.9.3).

Taking into account that the RRS is usually broadened in the amplified region, it is acceptable tocarry out the test at the center frequency of the broadened region and at frequencies spaced 1/3octave interval apart (or closer) until the amplitled area of the spectra is covered (see figure 1). Thisguards against the possibility that some critical frequencies are undetected during the investigationresponse test. Specimens having a critical frequency shall be tested at that frequency and at twoadjacent frequencies for which the TRS of the test wave (at critical frequency) is reduced by a

factor of m /2(see figure 1). In this case, it is suggested that the resonance search is repeated toverify that the critical frequency remains in the interval defined by the adjacent frequency.

The tests may consist of the application of a train of at least five sine beats or sine dwell (seefigures 2 and 3) at each frequency with a pause between any sine beat or sine dwell, in order tohave no significant superposition of equipment response.

Each sine beat (or sine dwell) should have a sufficient intensity and number of cycles (usually 5 to10) to produce a TRS according to the above criteria. For a given peak amplitude of the sine beat orsine dwell the conservatism of the test increases as the number of cycles increases (see figure 11).

6.5.4 Other waveforms

Other waveforms can be used if justifietin accordance with the requirements of 6.5.1. If decayingsine waves are used, the same criteria applies; the peak acceleration of decaying sine waves shallcorrespond to the ZPA value of the response spectra.

In any case, the single signal (not the train) shall give a TRS that envelops the RRS at testingfrequency and at ZPA. Sine sweep tests at a sweep rate not greater than 2 octaves per minute mayalso be used in the frequency range of interest. The sweep rate should be chosen according to thedamping value of the equipment. The TRS shall be evaluated around any single frequency.

24

. &<

IS 14989:2001 --- ..—IEC 60980(1989)

7 Documentation- --q

.1

Documentation to substantiate qualification should include:

7.1 General

- Details of the equipment ( 4.2. 1)- Details of the seismic specification- Details of the test criteria ( 4.2.3)

( 4.2.2)

- Documentation which identifies the equipment production route and the inspection whichapplies to it.

7.2 Qualification by analysis ‘●

Details of the analysis should be presented in a step-by-step form which is readily auditable bypersons skilled in such analysis and should include a listing of the potential failure modesconsidered in the analysis where computer codes are used. A reference to a validation documentshall be provided.

If proof of performance is obtained by extrapolation from similar equipment, the data shall contain:

- description of both equipment- test data on original equipment;- a detailed description of the differences between the two equipmen~- justification that the differences do not degrade the seismic performance below acceptablelimits (may require some additional analysis or testing) including any additional supporting data.

.

7.3 Qu@ication by test

- Test facility:. Location. Test equipment and calibration

- Test methods and procedures- Test data (including proof of performance)- Results and conclusions (particularly natural frequencies and maximum accelerations such ascomparison of TRS and RRS)- Production inspection data for the equipment which was tested- Ageing: Information on ageing procedures.

7.4 Continuiy

The documentation shall enable the qualification to be extended to the series production of theequipment.

25

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IS14989:2001

IEC

60980(1989)

%

—

V.

I/

I

.--.

iIIIII..—

.--—.

‘–-–-–-–-–-–-T-–-–

~II

—I

II

I

II

I

I\

\/

/q

\\

7I

II

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II

b,1

l\

--—-4-1.i

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1stbeat . Pause+

2ndbeat +Pause+ 3rdbt + ‘au”+‘“kat +Pause

/ Modulatingfriquency

rest frequencyf is thetestfrequency

wFive loadcycles

- 5th beat+

e

Figure 2- Train of five beats with five load cycles

IS 14989 :2001

IEC 60980(1989)

Five maximum-amplitudecycles/ \

———— ——.

-P-

-.. ___

1

,

. —

“-

.- —— - --

Figure 3- Sine dwell

-.

1/3 1/3 ~ Octavec 1- 1 .

P

Frequency

Figure 4 -,Types of response spectrum envelopes

28

—....—IS 14989:2001

IEC 60980(1989)

Acceleration(cm. S-2).101

i

Time (s)EL—+—+—+ 1 I I I I I *’02 4 6 8 10 12 14 16 18 20

Figure 5- Time history

,.

29

IS 14989:2001

IEC 60980(1989)

. &

Section 1 Secuon N

1)Large eqmpment

Sub-component1—.— —

!)Complex eqmpment—.— —

Sub-componentN

I

3) Multlple eqmpment Commonparts

1

2

IT

I Specflc parts I

Figure 6- Schematic procedures to dissociate large, complex ormultiple equipment into several sub-assemblies

.c -

I I Sub-assemblies I

Figure 7- Seismic loading of sub-assemblies

30

K 14989:2001

IEC 60980(1989)

tVertical applicableRRS

HorizontalapplicableSRS

A A A

4

Im.

Acceleration

4

‘v’--Fy-%.i 1

Intervalof uncertainty

Frequency

. -

Figure 8- Applications of horizontal and vertical RRS acceleration

31

IS 14989:2001

IEC 60980(1989)

. &

...-

I)Sub-assembly AVerificationand, if necessary,additionalactionstoensure that the availablequalificationcovers theboundary conditionsand couplingeffectsof

- removal of B- mounting of C

2) Sub-assembly C

P

:,,,.,.,.,.,.................

Qualificationof C to the conditionsresulting ~ c!from the mounting in A. ,::::::::::<:~::.,,:,

A

Figure 9- Equipment resulting from the modification of sub-assemblies

New

Verificationand, if necessary,additionalactions to ensure that availablequalificationof the constituentsA and B coverstheboundaryconditionsand couplingeffectsresulting from their assembly.

D%

Figure 10- Equipment resulting from the assembly of two or more sub-assemblies

32

IS 14989:2001

IEC 60980(1989)

4-

..

—-J

.

i%

40

30

20

10

5

0

ification factor

20 cycles/ sine beat

Continuous sine

\\\\\\

, 10 cycles/sine beat

Typicaltimehistory(natural)

/Fivecycles/sine beat

\\\

----- —— ___ ____

Three cycles / sine beat

i- -—-

———— —.

o 5% 10% 15%Percentof criticaldamping

..-.

Figure 11- Wave amplification factors

33

IS 14989:2001

IEC 60980(1989)

ANNEX A

QUALIFICATION BY EXPERIENCE

A.1 Introduction

There are many types of equipment which are similar in function and physical characteristics toequipment that has been previously qualified by testing, analysis, or a combination of both testingand analysis.

In addition, other equipment types are similar to equipment that has been in service for variousperiods of time and has been exposed to inplant vibration and natural seismic disturbances.

Therefore, qualification of these equipment types may be achieved by justifying their similaritywith previously qualified equipment or with equipment that has been exposed to other more severeenvironments. Simihuity of the excitation environment and of the equipment characteristics shall beestablished by techniques that can be technically justified. Due consideration to changes in designand manufacturing techniques shall be considered as part of the technical justification supportingsimilarity.

A.2 Experience data

Experience data may be derived from a variety of sources.

It may be:

a) analysis or test data from previous qualillcation programs;

b) documented data from equipment in facilities which have experienced natural earthquakes;

c) data from operating dynamic loading or other dynamic environments.

Depending on the source and level of documentation detail available, various approaches areappropriate. The following sub-clauses provide additional detail specific to each case.

A .2.1 Previous quahfication

Many seismic and dynamic qualification programs have been conducted for various safetyequipment items by the nuclear industry and can be used to develop an experience data base. Someof these equipment items may have been qualified by incorporating a full test program along withpreliminary exploratory (resonance search) tests. Others have been qualified using analyticaltechniques as described in clause 5 or by using a combined test and analytical technique. In order touse this experience data base, the input motions for which the equipment was previously qualifiedshall have been clearly documented, together with pertinent qualification parameters, such asresonant frequencies, damping and response throughout the equipment.

A .2.2 Earthquakes

Another type of experience data consists of the documented performance of equipment in facilitiesthat have been subjected to an earthquake. The data base equipment can be identical or similar(construction, dynamic response, etc.) to the equipment being qualified.

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It is preferable that the earthquake be qualified by recorded measurement of the earthquake inducedmotion at, or near, the equipment mounting location. However, it is recognized that this is not

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generally available; therefore, alternatively a documented conservative estimate of input motion may::,

be generated by extrapolation or interpolation of measurements elsewhere (see 6.3.1).

A.2. 3 Other experience

The approach described above for natural earthquake data may also be applied to the use ofoperating dynamic loading or other documented dynamic environments as a basis for qualification.In any case, the principle of similarity shall be used to justify the approach.

A.3 Similarity

Qualification by the use of extrapolation from experience data shall be based on the concept ofdynamic similarity. This concept recognizes that the qualification process for equipment iscomprised of the following basic factors:

a) excitation,b) physical system (dynamic properties and operability),c) dynamic response.

Generally, establishment of the dynamic similarity for the excitation and physiczd system will allowa successful qualification to be established by extrapolation from experience data. For example,assume that a given equipment item has been qualified to a specified excitation. Then, a secondequipment item, whose physical system similarity can be established, is also qualified to the sameexcitation. Another example would be where two or more identical, or at least dynamically similar,items have each been qualified to different excitations. They can both have been qualified foranother composite excitation, which can be shown to be similar to the original different excitations.

A.3. 1 Excitation

Similarity of excitation constitutes likeness of parameters such as spectral characteristics, duration,direction of excitation axes, and location of measurement for the motions relative to the equipmentmounting. Ideally, the experience response spectra (ERS) should be as alike as is practical fordifferent excitations whose similarity is to be established.

However, a conservative composite excitation can be generated by extrapolations or interpolationsof data whose parameters are not identical but are justifiable. For example, estimates may be basedon measurements elsewhere on the structure or on other structures in the vicinity of the givenequipment, if the estimates can be justified by calculations based on sound engineering methodsusing geophysical models, structural models, or both as applicable.

Likewise, excitations whose spectral content is significantly different may be used to generatelower level composite estimates providing that approximations for multimode response or crossaxis coupling or both are accounted for. Justification for such approximations shall consider theabsence of modal excitation caused by mismatch of spectral content in the composite RRS. Thus,the interaction of excitation characteristics and dynamic properties for the specimen shall be givenconsideration.

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IS 14989:2001

IEC 60980(1989)

Duration of a composite excitation shall be similar to that from which it is derived. Furthermore, toprovide for proper vibration buildup and low cycle fatigue effects, as with qualification by testing,any constituent experience data shall be based on a minimum of 15 s of strong motion duration or ajustifiable equivalent.

The qualification shall account for the ageing effects of exposure to the required normal andabnormal conditions such as normal plant vibrations and the required S 1. If no S 1 can bedocumented in the data derived from experience, then the lack of fatigue effects shall be justified ora fatigue analysis shall be performed.

A.3.2 Physical systems

Equipment similarity shall be established for an equipment assembly, or a device or sub-assembly(including mounting), depending on the configuration of the new equipment to be qualified. For acomplete assembly, similarity may be demonstrated through comparison of make, model and serialnumbers and consideration of dynamic properties and construction.

Since the final objective of qualification by the similarity method includes consideration of theexpected dynamic response, a rational approach can be made to establish similarity of dynamicstructural properties by an investigation of physical parameters of equipment systems. This can bedone by comparing the predominant resonant frequencies and mode shapes. These dynamiccharacteristics are dependent on parameters such as:

a) equipment physical dimensions;

b) equipment weight, its distribution and center of gravity;

c) equipment structural load transferring characteristics and stiffness to resist seismic excitation; .-

d) equipment base anchorage strength and stiffness to assure both structural integrity andadequate boundary conditions; and !

e) equipment interfaces with adjacent items or connecting accessories such as cables andconduits.

The relative difference, or dissimilarity, of all the above physical parameters makes it necessary toensure that adequate similarity exits between equipment assemblies. In addition, it should beensured that changes from the original data base equipment do not result in the formation ofpreviously nonexistent resonances and do not introduce new mechanisms for malfunction.

For the equipment where seismic qualification can be proved by showing that individual safetydevices are performing properly during the earthquake, a device or subassembly similarityevaluation approach may be considered. The similarity of physical systems will be applied for theindividual devices. In this case, the similarity in mechanical device and electrical operatingprinciples shall first be addressed.

The physical system parameters, as applicable to equipment assemblies discussed above, may notbe obvious, or may be difficult to define such as in an analysis or engineering judgementjustification. Therefore the justification of similarities relies on the careful examination of thedynamic properties, anchorage, and the mechanical and electrical operating principles as applicableto the device. In any case, an appropriate physical parameter data base shall be used to demonstratethat similar equipment behavior will result between the data base equipment and the equipmentunder investigation. For complex devices, a test will be required to show proper justification.

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A.3.3 Dynamic response,

;,..>

A physical system response can be described using the same quantities as an excitation (i.e. y....

duration, frequency content, amplitude, etc.), or using a physical system description giving failuremodes, failure criteria and criteria for acceptance or rejection.

When the physical system characteristics are known through the experience data (by any one of thepreviously mentioned methods of 5.2.1 through 5.2.3) and the excitation characteristics are alsoavailable, then the system response can be evaluated and extended towards similar systems.

On the other hand, there are occasions where only response and physical system characteristics areavailable. For these situations, the excitation requirement can be evaluated in the light of the knownresponse quantities and the physical system characteristics (obtained by methods 5.2.1 through5.2.3). Such information for the input excitation may then be used to qualify similar equipment.

A.3.4 Operability

Equipment being qualified shall be capable of performing its safety function during and after anearthquake. The safety function during the earthquake may, or may not, be the same as after theearthquake. Therefore, for each qualification, the safety function shall be defined for conditionsboth during and after the earthquake. The experience data shall. provide the documented evidence tosupport the demonstration of proper operability, as defined for each application. Where an activefunction, or the absence of a spurious function, is required during the earthquake, the experiencedata shall provide sound evidence that the equipment performed as required in a similar electricalsystem.

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Bureau of Indian Standards

BIS is a statutory institution established under the Bureau of Indian Standards Acl,. 1986 to promoteharlnonious development of the activities of stardardization, marking and quality certification of goods andattending to connected matters in the country.

Copyright

B] S has the copyright of all its publications. No part of these publications may be reproduced in any formwithout the prior permission in writing of BIS. This does not preclude the free use, in the course ofimplementing the standard, of necessary details, such as symbols and sizes, type or grade designations.Enquiries relating to copyright be addressed to the Director (Publication), BIS.

Review of Indian Standards

Amendments are issued to standards as the need arises on the basis of comments. Standards are also reviewedperiod icall y; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standardsshou]d ascertain that they are in possession of the latest amendments or edition by referring to the latest issueof’ B1S Handbook’ and’ Standards: Monthly Additions’.

This Indian Standard has been developed from Dot: No. LTD 26 (14 13).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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